I actually just spent yesterdy (the whole of it) trying to recreate the style from the dino-map. I almost lost my mind. My template was this and this.

No matter what I did, it always looked crappy and was way too much work. What I came up with was that, dunno if that would work for you:

Click image for larger version. 

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The ridgeline in the middle is just for guidance, in this case I just forgot to put it on an extra layer, that's why it's still there...
I used a soft brush with a fine texture and low opacity and flow. Maybe that's something to work off.